An X-ray arrangement is generally known. Reference is made purely by way of example to DE 10 2011 081 280 A1 and U.S. Pat. No. 4,500,142 A.
In the operation of an X-ray arrangement, a cathode is used to produce an electron beam which is directed onto an anode. The point on which the electron beam is incident is termed the focal point. The X-rays are generated in the focal point.
The electron beam heats up the focal point. In order to prevent overheating of the focal point, the anode is often designed as a rotating anode which is rotated about an axis of rotation during operation. The rotation is produced by way of an electrical machine, the rotor of which is disposed together with the rotating anode inside a vacuum vessel and the stator of which is disposed outside the vacuum vessel.
Optimum imaging requires that during operation of the X-ray arrangement the focal point is static, i.e. does not move, or at least moves only slightly relative to the X-ray arrangement which, as an entity, does not rotate about the axis of rotation of the X-ray arrangement. As the X-ray-generating electron beam can be affected by electromagnetic fields, it is therefore necessary to keep the effect of the electromagnetic fields as constant as possible.
An important influencing factor are the stray fields emerging from the stator when the rotor is being driven. These stray fields cause focal point movements which can be in the region of several 100 μm viewed both in the direction around the axis of rotation and orthogonally thereto. The resulting imaging disturbances and errors are often non-negligible, but at the very least disadvantageous.
From DE 10 2011 081 280 A1 it is known to implement the winding system of the stator as a yoke winding. Such a winding system ensures that the focal point moves less than approximately 50 μm both in the direction viewed around the axis of rotation and orthogonally thereto. However, a yoke winding is complicated to manufacture and therefore cost-intensive.
It has already also been proposed to reduce the current applied to the winding system of the stator during active operation of the X-ray arrangement, i.e. while the X-rays are being emitted, or even disconnect it completely.